The conventional motorcycle lock has a very weak structure which may be broken easily, further bicycles have also no effective lock to protect bicycles from being stolen. Various locks have been developed for this reason, one of the kind is a U-shaped lock, as shown in FIG. 6 which includes a lock core 94 mounted at the center portion of a lock seat 91 to link two latches 93 at respective sides of the lock seat 91. The lock seat 91 is mounted in a lock barrel 92. Both of the lock seat 91 and the lock barrel 92 have a hole 911 and 921 at the center bottom portion and two holes 912 and 922 at respective ends for a pair of lock bars 95 to seat therein. The lock seat 91 also has a slot 913 for a pair of latches 93 to seat therein. Whereas the corresponding ends of the latches 93 are formed with a blind hole 931 to receive a spring 932 and a pin 933 therein, respectively. Each latch 93 has also formed with a recess 934 for a knob 941 of the lock core 94 to rest therein.
Upon studying the relation between the latch which when in a locked status, as shown in FIGS. 7 and 8, the two latches 93 are controlled merely by the spring 932 urging the latch 93 to insert into a recess 951 of the lock bar 95 to constrain movement of the lock bar 95. However, the recess 934 is to receive the knob 941 of the lock core 94 to seat therein, there is an extra space left which allows the latch 93 to move rearward, and owing to the spring 932 is not a fixed status, when the spring 932 is urged rearward, the latch 93 retreats from the lock bar 95 which means that by plunging the lock from outside, a reflection force will force the latch 93 to retreat from the recess 951 thus, the lock bar 95 is free for removal from the lock barrel 92.